1. Field of the Invention
The present invention relates to rack housing for user reconfigurable EDP systems.
2. Description of the Prior Art
Modern data processing systems are comprised of electronic circuits mounted on a plurality of printed circuit boards (PWA) housed in a box shaped frame having an open front and arranged therein on suitable parallel tracks. The tracks comprise racks for the mechanical positioning of the several PWAs. The PWAs, singly or in sets, carry out various functions such as the system central unit or of peripheral unit controllers. The frame front is open to allow the insertion of the several PWAs on the tracks and may be closed by a cover fixed by screws or by other fixing means such as the so-called "fasteners". Modern data processing systems are reconfigurable, to permit increased performance and meet the specific needs of the user by the addition of electronic circuits. This may be done by the addition of PWAs in the frame. Accordingly the frame is intended to contain a predetermined number of PWAs while the number actually inserted may vary from a minimum M&lt;N up to N according to the specific needs of the user. The minimum number M of PWAs comprises the minimum system configuration, that is, a set of electronic circuits which may be tested and which is able to operate in a correct way according to minimum user requirements.
In conventional manufacturing and distribution of such equipment the warehouse administration is affected by important cost problems. There are two approaches which may be followed.
According to a first approach the EDP systems are assembled with minimum configuration tested and packed, in order to be ready for distribution, then stored. The system reconfiguration, according to the user needs, is performed at the user site by specialized technical people which adds PWAs to the system. The cost of the specialized operation is high and does not conform to the technological trends of supplying products of the "plug and play" type which do not require specialized technical support for their installation.
According to a second approach the EDP systems are assembled in any possible configuration, tested, packed and stored. In this case a configured model suitable for any user need is available, but this causes an increase of the fixed store inventory. Moreover, in case the user-needs evolve, the already installed system must be substituted or a specialized operation is again required. To overcome such problems an embodiment has been recently suggested of a system where the reconfiguration can be performed by the user himself, if he is provided with a system having a minimum configuration and additional PWAs. The reconfiguration operation must be easy, must not require special devices and complicated assembly which may increase the cost of the product.
It is known in the art, for example from U.S. Pat. Nos. 4,334,261 and 4,301,494, that the open front of a rack housing for several PWAs can be closed by a plurality of cover plates, one for each PWA, fixed by knurled grips or fasteners. This solution permits possible system reconfiguration to be made by the users, but the equipment assembly becomes longer and more complicated, therefore causing a cost increase when compared with the cost of similar equipment provided with a single cover for the whole rack housing.
In both these cases the user is not prevented from removing the PWAs already installed. Further the repetitive modularity of the cover plates described in the above-mentioned patents can mislead the user in the reconfigurating operation.